score:8
The general rule, in daytime, is that a single “t+” ticket is valid for either:
There are a few exceptions, like for the Orlybus and Roissybus lines. The total duration of the trip should be less than 1h30. Transfers from RER or metro to/from bus or tramway require a new ticket.
Noctilien night bus lines follow the same rules, however only lines with 2-digit numbers and line N135 can be used with a single t+ ticket. All other lines require two tickets.
Massy-Palaiseau is served by night buses N63 and N122. Using N63 will cost you a single ticket. Using N122 would require two.
The RATP journey planner is incorrect: it states that you can do the trip using N122 with a single ticket, which isn’t true according to the detail page for the t+ ticket.
Of course, RATP (operator) and Île-de-France Mobilités (organising authority) don’t agree. While they agree on the one or two ticket rule depending on the line, RATP explicitly says transfers are possible while IdFM says no, you need a new ticket for each bus. However the T&Cs on the same site say you can (and you just need to validate a second ticket if you switch from a single-ticket line to a two-ticket line).